1. Field of the Invention
This invention relates to fittings for plastic insulated electric cables in general and more particularly to the design of prefabricated fittings or fitting parts with an elastic insulating body and metallic housing.
2. State of the Art
For plastic insulated medium and high voltage cables, especially for such cables with insulation of thermoplastic or cross-linked polyethylene, fittings and fitting parts have recently been developed which are pushed onto the appropriately prepared cable end or are plugged into the appropriately processed cable ends. These fittings consist essentially of an elastic insulating body consisting of an ethylene-propylene terpolymer rubber or silicone rubber and are provided with elements for controlling the electric field. Their inside hole is smaller than the outside diameter of the respective prepared cable conductor with which they are used. Upon pushing onto the cable conductor, or plugging a cable end in, the fitting parts are expanded enough that a press fit without voids is obtained on the conductor insulation.
To design such fittings or fitting parts with contact protection and to allow a metallic through connection of the cable shields, metallic housings have been provided. If the housing is of tubular design, a compressible foam layer or an air cushion arranged between elastic ribs is disposed between the housing and the elastic insulating body, so as to avoid a narrowing of the radial elastic expandability of the insulating body (DE-OS No. 27 26 402, DE-OS No. 27 26 403). These measures, however, increase the thermal resistance of the fitting as a whole.
A cable fitting in the form of a connecting sleeve, made using casting resin is also known, in which a metal cylinder is arranged within the housing for connecting through the cable shields. This cylinder is formed of a piece of expanded metal (DE-AS No. 16 65 218). The cutouts in the cylinder ensure that the cylinder is embedded in the cast resin body.
A shielded electric cable is furthermore known, in which the shield consists of a metal strip which is subdivided into a number of narrow ribbons which are connected by transverse bridges by elongated narrow holes extending in the lengthwise direction. Because of the perforation it is possible to contact or twist the shielding band to form an electric conductor similar to individual wires (DE-OS No. 24 19843).
Starting from a fitting for plastic insulated cables, especially medium or high voltage cables, which consists of an elastic, prefabricated insulating body which is provided with a hole and may contain an electrical connecting element, with a tubular metallic housing, it is an object of the present invention to reduce the thermal resistance between the insulating body and the metallic housing without, at the same time, narrowing down the radial elastic expandability of the insulating body.